JP6208503B2

JP6208503B2 - Wireless power receiving apparatus, control circuit and control method thereof

Info

Publication number: JP6208503B2
Application number: JP2013188721A
Authority: JP
Inventors: 大介内本; 竜也岩▲崎▼
Original assignee: ローム株式会社
Priority date: 2013-09-11
Filing date: 2013-09-11
Publication date: 2017-10-04
Anticipated expiration: 2033-09-11
Also published as: KR101976909B1; TW201513525A; KR20160053994A; CN105409086A; US20190123582A1; JP2015056959A; US10199866B2; WO2015037362A1; CN105409086B; US20160197513A1; TWI629845B

Description

The present invention relates to a wireless power feeding technique.

In recent years, contactless power transmission (also referred to as non-contact power feeding or wireless power feeding) has begun to spread in order to supply power to electronic devices. In order to promote mutual use between products of different manufacturers, the WPC (Wireless Power Consortium) was organized, and the international standard Qi (Qi) standard was formulated by WPC.

FIG. 1 is a diagram illustrating a configuration of a wireless power feeding system 100 compliant with the Qi standard. The power supply system 100 includes a power transmission device 200 (TX, Power Transmitter) and a power reception device 300 (RX, Power Receiver). The power receiving device 300 is mounted on an electronic device such as a mobile phone terminal, a smart phone, an audio player, a game device, or a tablet terminal.

The power transmission device 200 includes a transmission coil (primary coil) 202, a driver 204, a controller 206, and a demodulator 208. The driver 204 includes an H-bridge circuit (full-bridge circuit) or a half-bridge circuit, and applies a drive signal S 1, specifically a pulse signal, to the transmission coil 202. An electromagnetic field power signal S2 is generated. The controller 206 controls the power transmission apparatus 200 as a whole. Specifically, the controller 206 changes the transmission power by controlling the switching frequency of the driver 204 or the switching duty ratio.

In the Qi standard, a communication protocol is defined between the power transmission device 200 and the power reception device 300, and information can be transmitted from the power reception device 300 to the power transmission device 200 using the control signal S3. The control signal S3 is transmitted from the reception coil 302 (secondary coil) to the transmission coil 202 in the form of AM (Amplitude Modulation) modulation using backscatter modulation. The control signal S3 includes, for example, power control data (also referred to as a packet) for instructing the amount of power supplied to the power receiving apparatus 300, data indicating unique information of the power receiving apparatus 300, and the like. The demodulator 208 demodulates the control signal S3 included in the current or voltage of the transmission coil 202. The controller 206 controls the driver 204 based on the power control data included in the demodulated control signal S3.

The power receiving device 300 includes a receiving coil 302, a rectifier circuit 304, a capacitor 306, a modulator 308, a secondary battery 310, a controller 312, and a charging circuit 314. The reception coil 302 receives the power signal S <b> 2 from the transmission coil 202 and transmits a control signal S <b> 3 to the transmission coil 202. The rectifier circuit 304 and the capacitor 306 rectify and smooth the current S4 induced in the receiving coil 302 in accordance with the power signal S2, and convert it into a DC voltage.

The charging circuit 314 charges the secondary battery 310 using the power supplied from the power transmission device 200.

The controller 312 monitors the power supply amount received by the power receiving apparatus 300 and generates power control data (control error value) instructing the power supply amount accordingly. The modulator 308 modulates the control signal S3 including the power control data and modulates the coil current of the reception coil 302, thereby modulating the coil current and the coil voltage of the transmission coil 202.

The above is the configuration of the power feeding system 100. FIG. 2 is a flowchart showing an operation sequence of the power feeding system 100. The state of the power transmission device 200 is large, and is divided into a selection phase (Selection Phase) φ1, a power transmission (Power Transfer) phase φ2, and an authentication and configuration phase (Identification & Configuration Phase) φ3.

First, the power transmission phase φ2 will be described. The power transmission device 200 (TX) starts power transmission to the power reception device 300 (RX) (S100). A control signal S3 indicating the current power transmission state from the power receiving device RX is fed back to the power transmitting device TX (S102). The power transmission device TX adjusts the amount of power transmission based on the control signal S3 (S104).

The power transmission device TX transmits a control signal S3 indicating the completion of charging from the power reception device RX (S106), or that the power reception device RX has been removed from the power supply range of the power transmission device TX based on a communication timeout error. When detected (S108), the power transmission device TX stops power transmission and enters the selection phase φ1.

Next, the selection phase φ1 will be described. The power transmission device TX transmits a power signal S2 at predetermined time intervals (object detection interval, for example, 500 msec), and checks whether or not the power reception device RX is present (S200). This is called an analog pin phase.

When the power receiving device RX is detected (S202), the process proceeds to the authentication / setting phase φ3 and the digital pin phase (Digital Ping Phase) is executed (S204). In the subsequent authentication and configuration phase (Identification & Configuration Phase), the power transmitting apparatus TX receives the individual information of the power receiving apparatus RX (S206). Subsequently, information on power transmission conditions is transmitted from the power receiving device RX to the power transmitting device TX (S208), and the process proceeds to the power transmission phase φ2. The operation sequence of the power transmission device 200 has been described above.

JP 2013-38854 A

As a result of studying such a power supply system 100, the present inventors have recognized the following problems.

The charging circuit 314 can be switched between constant current (CC) charging and constant voltage (CV) charging according to the state of the secondary battery 310, and according to the remaining battery level during CC charging. Thus, the amount of charging current supplied to the secondary battery 310 is changed.

FIG. 3 is an operation waveform diagram of the power receiving device 300 of FIG. In the steady state, the current supplied from the rectifier circuit 304 to the capacitor 306 and the current supplied from the capacitor 306 to the charging circuit 314, that is, the charging current Ibat are balanced, and the rectified voltage Vrect generated in the capacitor 306 is a target level. Has been stabilized.

Here, the current supplied from the rectifier circuit 304 to the capacitor 306 depends on the power supplied from the power transmission device 200 to the power reception device 300, that is, is controlled based on the control signal S3. When the charging circuit 314 increases the charging current Ibat, a large current is drawn from the capacitor 306. As a result, when the rectified voltage Vrect decreases, the control error value included in the control signal S3 increases, and feedback is applied so that the power supplied from the power transmitting apparatus 200 to the power receiving apparatus 300 increases. Since the feedback speed is limited by the communication speed of the control signal S3 and the time until the power transmission apparatus 200 is stabilized at a new operating point, if the charging current Ibat fluctuates rapidly, the feedback cannot follow. The rectified voltage Vrect may deviate significantly from its target value. If the fluctuation amount of the rectified voltage Vrect is large or the fluctuation waveform is steep, the AM modulation of the control signal S3 using the backscatter modulation is hindered, and the power transmission apparatus 200 cannot correctly receive the control error value. That is, a sharp change in the charging current Ibat may cause the feedback loop to be interrupted. When the interruption of communication between the power transmission device 200 and the power reception device 300 continues for a predetermined timeout time, the power transmission device TX stops power transmission and returns to the selection phase φ1.

Such a problem should not be regarded as a common technical recognition of those skilled in the art.

SUMMARY An advantage of some aspects of the invention is to provide a power receiving apparatus capable of stabilizing communication with a power transmitting apparatus.

One embodiment of the present invention relates to a control circuit used in a wireless power receiving apparatus. The wireless power receiving apparatus includes a receiving coil, a rectifying circuit that is connected to the receiving coil and generates a rectified voltage, a charging circuit that receives the rectified voltage and charges a battery, and is connected to the receiving coil and receives the rectifying coil based on a control value. And a modulator for transmitting a control packet including a control value to the wireless power transmission device. The control circuit includes a charge control unit that controls a charging current supplied to the battery from the charging circuit, and a control error value that indicates a transmission power amount from the wireless power transmitting apparatus based on an error between a current rectified voltage and a target value thereof. A power control unit that generates and outputs a control value to the modulator. The charging control unit changes the charging current when the absolute value of the error is smaller than a predetermined threshold value.

According to this aspect, when the absolute value of the error is larger than the threshold value, by maintaining the set value of the charging current, the rectified voltage deviates significantly from the target value or the rectified voltage changes with a steep waveform. Thus, communication between the power transmission device and the power reception device can be stabilized.

When changing the charging current from the initial value to the final value, the charging control unit changes the charging current stepwise from the initial value toward the final value through a plurality of intermediate values provided between them, and Each time the charging current is changed by one step, the charging current may be changed to the value of the next step by waiting until the absolute value of the error becomes smaller than the threshold value.

The charging control unit may change the charging current in units of a predetermined minimum step.

The control circuit may conform to the Qi standard.

The control circuit may be integrated on a single semiconductor substrate.
“Integrated integration” includes the case where all of the circuit components are formed on a semiconductor substrate and the case where the main components of the circuit are integrated. A resistor, a capacitor, or the like may be provided outside the semiconductor substrate. By integrating the circuit as one IC, the circuit area can be reduced and the characteristics of the circuit elements can be kept uniform.

Another aspect of the present invention relates to a wireless power receiving apparatus. The wireless power receiving apparatus includes a receiving coil, a rectifying circuit that is connected to the receiving coil and generates a rectified voltage, a charging circuit that receives the rectified voltage and charges a battery, and is connected to the receiving coil and receives the rectifying coil based on a control value. And a modulator that transmits a control packet including a control value to the wireless power transmitting apparatus, and a control circuit described in any of the above.

Another aspect of the present invention is also a wireless power receiving apparatus. The wireless device includes a receiving coil, a rectifying circuit that is connected to the receiving coil and generates a rectified voltage, a charging circuit that receives the rectified voltage and charges a battery, and is connected to the receiving coil and is configured to receive the rectified voltage based on a control value. A modulator that modulates voltage or current and transmits a control packet including a control value to the wireless power transmission device, a charge control unit that controls a charging current supplied from the charging circuit to the battery, a current rectified voltage, and a target value thereof And a power control unit that outputs a control error value indicating a transmission power amount from the wireless power transmission apparatus based on the error to the modulator as a control value. The charging control unit changes the charging current so that the absolute value of the error does not exceed a predetermined allowable value.

According to this aspect, by changing the charging current while monitoring the error of the rectified voltage, it is possible to prevent the rectified voltage from significantly deviating from the target value or the rectified voltage from changing with a steep waveform, thereby enabling the power transmission device And the power receiving device can be stabilized.

When changing the charging current from the initial value to the final value, the charging control unit repeats the step of changing the charging current by a predetermined amount and the step of waiting until the absolute value of the error becomes smaller than a predetermined threshold value. Also good.

The wireless power receiving apparatus may conform to the Qi standard.

It should be noted that any combination of the above-described constituent elements, and those in which constituent elements and expressions of the present invention are mutually replaced between methods, apparatuses, systems, and the like are also effective as an aspect of the present invention.

According to an aspect of the present invention, communication with a power transmission device can be stabilized.

It is a figure which shows the structure of the wireless electric power feeding system based on Qi specification. It is a flowchart which shows the operation | movement sequence of the electric power feeding system of FIG. It is an operation | movement waveform diagram of the power receiving apparatus of FIG. It is a circuit diagram which shows the structure of the wireless power receiving apparatus which concerns on embodiment. FIG. 5 is a waveform diagram illustrating an operation of the power receiving device of FIG. 4.

The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. The embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

In this specification, “the state in which the member A is connected to the member B” means that the member A and the member B are electrically connected to each other in addition to the case where the member A and the member B are physically directly connected. It includes cases where the connection is indirectly made through other members that do not substantially affect the general connection state, or that do not impair the functions and effects achieved by their combination.
Similarly, “the state in which the member C is provided between the member A and the member B” refers to the case where the member A and the member C or the member B and the member C are directly connected, as well as their electric It includes cases where the connection is indirectly made through other members that do not substantially affect the general connection state, or that do not impair the functions and effects achieved by their combination.

FIG. 4 is a circuit diagram showing a configuration of a wireless power receiving apparatus (hereinafter simply referred to as a power receiving apparatus) 300 according to the embodiment. The power receiving apparatus 300 is used in the power supply system 100 that conforms to the Qi standard of FIG.

The power receiving device 300 includes a receiving coil 302, a rectifier circuit 304, a capacitor 306, a modulator 308, a charging circuit 314, a secondary battery 310, and a control circuit 320.

The reception coil 302 is provided to receive the power signal S2 transmitted from the power transmission device 200 and to transmit a control signal (control packet) S3. The rectifier circuit 304 is connected to the receiving coil 302 and generates a rectified voltage Vrect. A smoothing capacitor 306 is connected to the output of the rectifier circuit 304.

The charging circuit 314 receives the rectified voltage Vrect and charges the secondary battery 310. The charging circuit 314 can operate in a mode instructed by the control circuit 320 described later, and the charging current Ibat can also be adjusted based on a command value from the control circuit 320.

The modulator 308 is connected to the reception coil 302, modulates the voltage or current of the reception coil 302 based on the control value S5, and transmits a control signal S3 including the control value S5 to a wireless power transmission apparatus (not shown).

The control circuit 320 includes a charge control unit 322 and a power control unit 324, and is integrated on a single semiconductor substrate. The charging circuit 314 controls the charging circuit 314 and adjusts the charging current Ibat supplied to the secondary battery 310. Specifically, the optimum charging current Ibat is determined based on the state of the secondary battery 310, for example, the battery voltage Vbat, the remaining amount of the secondary battery 310, etc., and the current control data S6 indicating the charging current Ibat is charged. Output to circuit 314.

The power control unit 324 generates a control error value CE that indicates the amount of transmission power from the wireless power transmitting apparatus based on the error dV = Vref−Vrect between the current rectified voltage Vrect and the target value Vref, and uses the control error value CE as the control value S5. Output to the modulator 308. The control error value CE is, for example, a value obtained by quantizing the error dV with 256 gradations (8 bits) from −128 to +128.

The charging control unit 322 changes the charging current Ibat when the absolute value | dV | of the error dV is smaller than a predetermined threshold value Vth. When the absolute value | dV | of the error dV is larger than the threshold value Vth, the charging current Ibat is maintained.

More preferably, when the charging control unit 322 changes the charging current Ibat from the initial value (current location) Istart to the final value Iend, a plurality of n intermediate values Im1, Im2, between the initial value Istart and the final value Iend. … Imn is set. Then, the charging control unit 322 changes the charging current Ibat from the initial value Istart to the final value Iend in a step shape through a plurality of intermediate values Im1, Im2,... Imn provided therebetween. Each time the charging control unit 322 changes the charging current Ibat by one step, the charging control unit 322 waits until the absolute value | dV | of the error dV becomes smaller than the threshold value Vth, and then the charging current Ibat is the value of the next step. To change.

The interval between the plurality of intermediate values Im1 to Imn may be equal to the minimum step (resolution) of the charging current Ibat that can be set in the charging circuit 314. For example, when the charging current Ibat can be selected between the minimum value 0A and the maximum value 2A in increments of dI = 100 mA, the interval between the intermediate values Im is 100 mA.

From another viewpoint, the charging control unit 322 changes the charging current Ibat in a pattern determined so that the absolute value | dV | of the error dV does not exceed a predetermined allowable value.

The above is the configuration of the power receiving device 300. Next, the operation will be described. FIG. 5 is a waveform diagram (solid line) showing the operation of the power receiving device 300 of FIG. In FIG. 5, the waveform corresponding to FIG. 3 is indicated by a one-dot chain line.

In order to clarify the effect of the power receiving device 300 according to the embodiment, the operation of the conventional power receiving device 300 will be described again with reference to the alternate long and short dash line. At time t0, the target value of the charging current Ibat changes from the current value (initial value) Istart to the next target value (final value) Iend. Conventionally, as indicated by the one-dot chain line, at time t0, the charging current Ibat is switched from the initial value Istart to the final value Iend, so that the rectified voltage Vrect is steeply and greatly increased from the target value Vref. As a result, there is a problem that communication between the power transmission device 200 and the power reception device 300 is interrupted.

In turn, the operation of the power receiving device 300 according to the embodiment will be described with reference to a solid line. When the charging current Ibat is changed from the initial value Istart to the final value Iend, a plurality of intermediate values Im1, Im2, Im3,... Are determined. For example, when Istart = 500 mA and Iend = 1100 mA, the charging current Ibat is switched stepwise in 6 steps in increments of 100 mA.

First, the charging current Ibat is set to the first intermediate value Im1 (= 600 mA). Thereby, the rectified voltage Vrect slightly decreases. When the error dV increases due to the decrease in the rectified voltage Vrect, the control error value CE increases. Thereby, the power transmission apparatus 200 increases transmission power. When this operation is repeated, the rectified voltage Vrect rises and approaches the target value Vref, and the control error value CE, which is an error dV thereof, decreases.

At time t1, when the control error value CE becomes smaller than the threshold value TH corresponding to the threshold voltage Vth, that is, when the absolute value | dV | of the error dV becomes smaller than the threshold voltage Vth, the charging current Ibat becomes the next. It is switched to the intermediate value Im2 (= 700mA). The control circuit 320 repeats this operation and changes the charging current Ibat to the final value Iend.

According to the power receiving device 300, when the absolute value | dV | of the error dV is larger than the threshold value Vth, the set value of the charging current Ibat is maintained, and the process waits until the absolute value | dV | Thus, it is possible to prevent the rectified voltage Vrect from significantly deviating from the target value Vref and the rectified voltage Vrect to change with a steep waveform, thereby stabilizing the communication between the power transmitting apparatus 200 and the power receiving apparatus 300.

After time t3, an operation for reducing the charging current Ibat is shown. For example, Istart = 1100 mA and Iend = 700 mA, and the charging current Ibat is switched stepwise in 4 steps in increments of 100 mA.

First, the charging current Ibat is set to the first intermediate value Im1 (= 1000 mA). As a result, the rectified voltage Vrect slightly increases. As the rectified voltage Vrect increases, the control error value CE decreases (its absolute value increases). Thereby, the power transmission apparatus 200 reduces transmission power. When this operation is repeated, the rectified voltage Vrect decreases and approaches the target value Vref, and the absolute value of the control error value CE, which is their error dV, decreases.

At time t4, when the control error value CE rises to the threshold value -TH, that is, when the absolute value | dV | of the error dV becomes smaller than the threshold voltage Vth, the charging current Ibat becomes the next intermediate value Im2 (= 900 mA). ). The control circuit 320 repeats this operation and changes the charging current Ibat to the final value Iend.

Thereby, communication between the power transmission device 200 and the power reception device 300 can be stabilized even when the charging current Ibat is decreased.

The present invention has been described based on the embodiments. Those skilled in the art will understand that these embodiments are exemplifications, and that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. By the way. Hereinafter, such modifications will be described.

(First modification)
In the embodiment, the charging current Ibat is gently changed both when the charging current Ibat is increased and when it is decreased. However, the present invention is not limited to this. For example, the charging current Ibat may be changed gently only when it is increased, and may be changed abruptly when it is decreased.

(Second modification)
In the embodiments, the wireless power transmission device conforming to the Qi standard has been described. However, the present invention is not limited to this, and the wireless power transmission device used in a system similar to the Qi standard or a standard that will be developed in the future. The present invention can also be applied to a compliant power transmission device 200.

Although the present invention has been described using specific terms based on the embodiments, the embodiments only illustrate the principles and applications of the present invention, and the embodiments are defined in the claims. Many variations and modifications of the arrangement are permitted without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 100 ... Power feeding system, 200, TX ... Power transmission apparatus, 201 ... Transmitting antenna, 202 ... Transmitting coil, 203 ... Resonance capacitor, 204 ... Driver, 206 ... Controller, 208 ... Demodulator, 300, RX ... Power receiving apparatus, 302 ... Reception Coil, 304 ... rectifier circuit, 306 ... capacitor, 308 ... modulator, 310 ... secondary battery, 312 ... controller, 314 ... charge circuit, 320 ... control circuit, 322 ... charge control unit, 324 ... power control unit, S1 ... Drive signal, S2 ... power signal, S3 ... control signal.

Claims

A receiving coil, a rectifying circuit connected to the receiving coil and generating a rectified voltage, a charging circuit receiving the rectified voltage and charging a battery, a voltage or current of the receiving coil connected to the receiving coil and based on a control value A control circuit for use in a wireless power receiving device, comprising: a modulator that modulates the wireless power transmitting device and transmits a control packet including the control value to the wireless power transmitting device,
The control circuit includes:
A charging control unit for controlling a charging current supplied from the charging circuit to the battery;
A power control unit that generates a control error value indicating a transmission power amount from the wireless power transmission device based on an error between the current rectified voltage and the target value, and outputs the control error value to the modulator as the control value;
With
The control circuit, wherein the charging control unit changes the charging current when an absolute value of the error is smaller than a predetermined threshold value.
When the charging control unit changes the charging current from an initial value to a final value,
From the initial value toward the final value, the charging current is changed stepwise through a plurality of intermediate values provided therebetween,
Each time the charging current is changed by one step, the process waits until the absolute value of the error becomes smaller than the threshold value, and changes the charging current to the value of the next step. Item 2. The control circuit according to Item 1.
The control circuit according to claim 2, wherein an interval between the plurality of intermediate values is equal to a minimum step of a charging current that can be set in the charging circuit.
4. The control circuit according to claim 1, wherein the control circuit conforms to a Qi standard.
The control circuit according to claim 1, wherein the control circuit is integrated on a single semiconductor substrate.
A receiving coil;
A rectifier circuit connected to the receiving coil and generating a rectified voltage;
A charging circuit that receives the rectified voltage and charges a battery;
A modulator that is connected to the receiving coil, modulates the voltage or current of the receiving coil based on a control value, and transmits a control packet including the control value to a wireless power transmission device;
A control circuit according to any one of claims 1 to 5;
A wireless power receiving apparatus comprising:
A receiving coil;
A rectifier circuit connected to the receiving coil and generating a rectified voltage;
A charging circuit that receives the rectified voltage and charges a battery;
A modulator that is connected to the receiving coil, modulates the voltage or current of the receiving coil based on a control value, and transmits a control packet including the control value to a wireless power transmission device;
A charging control unit for controlling a charging current supplied from the charging circuit to the battery;
A power control unit that generates a control error value indicating a transmission power amount from the wireless power transmission device based on an error between the current rectified voltage and the target value, and outputs the control error value to the modulator as the control value;
With
The wireless power receiving apparatus, wherein the charging control unit is configured to change the charging current so that an absolute value of the error does not exceed a predetermined allowable value.
When the charging control unit changes the charging current from an initial value to a final value,
Changing the charging current by a predetermined amount;
Waiting until the absolute value of the error is less than a predetermined threshold;
The wireless power receiving apparatus according to claim 7, wherein:
The wireless power receiving apparatus according to claim 8, wherein the predetermined amount is equal to a minimum step of the charging current that can be set in the charging circuit.
10. The wireless power receiving apparatus according to claim 7, wherein the wireless power receiving apparatus conforms to a Qi standard.
A method of controlling a wireless power receiving apparatus,
The wireless power receiving apparatus is connected to the receiving coil, the rectifying circuit connected to the receiving coil to generate a rectified voltage, the charging circuit that receives the rectified voltage and charges the battery, the voltage connected to the receiving coil, A modulator that modulates current and transmits packets to the wireless power transmission device;
The control method is:
Controlling a charging current supplied from the charging circuit to the battery;
Generating a control error value indicating an amount of transmission power from the wireless power transmission device based on an error between the current rectified voltage and the target value;
Controlling the modulator based on the control error value, and transmitting a control packet including the control error value from the receiving coil to the wireless power transmitting device;
With
The control method characterized in that the charging current changes when the absolute value of the error is smaller than a predetermined threshold value.
A method of controlling a wireless power receiving apparatus,
The wireless power receiving apparatus is connected to the receiving coil, the rectifying circuit connected to the receiving coil to generate a rectified voltage, the charging circuit that receives the rectified voltage and charges the battery, the voltage connected to the receiving coil, A modulator that modulates current and transmits packets to the wireless power transmission device;
The control method is:
Generating a control error value indicating an amount of transmission power from the wireless power transmission device based on an error between the current rectified voltage and the target value;
Controlling the modulator based on the control error value, and transmitting a control packet including the control error value from the receiving coil to the wireless power transmitting device;
Controlling a charging current supplied from the charging circuit to the battery so that the error does not exceed a predetermined allowable value;
A control method comprising:
The step of controlling the charging current, when changing the charging current from an initial value to a final value,
Changing the charging current by a predetermined amount;
Waiting until the absolute value of the error is less than the threshold;
The control method according to claim 11 , wherein:
The control method according to claim 13, wherein the predetermined amount is equal to a minimum step of the charging current that can be set in the charging circuit.